A study of the prior art relative to the manufacture or cordierite and cordierite-like ceramic units show that the ingredients are selected based on the use of the sintered ceramic unit. In general, the ingredients used in making the green units comprise clay, talc and alumina, which contribute the three oxides needed for cordierite namely magnesium oxide, alumina and silica sometimes referred to as the MAS system (magnesia-alumina-silica) (See U.S. Pat. No. 3,979,216 C. W. Fritsch).
Since cordierite in general has two main essential properties, namely, low thermal expansion and thermal shock resistance to varying degrees depending on the intended use of the ceramic unit made therefrom, the composition of the cordierite will vary accordingly.
For example, cordierite can be made by mixing pure oxides of magnesium, aluminum and silicon in proportions such as to give the desired cordierite composition (See U.S. Pat. No. 4,063,955). Obviously the cost of preparing such oxides can be very expensive. In an attempt to reduce the cost products readily available in nature such as clay which contains alumina and silica and talc which contains magnesia and silica have been used in association with pure alumina.
Variations of these three components and addition of other ingredients will be made depending on the specific properties desired in the cordierite ceramic products. For example, the replacement of part of the clay by calcined clay, part or all of the talc by calcined talc and part of all of the alumina by calcined alumina has been found useful in the preparation of catalytic converters for automobile exhaust systems as disclosed in U.S. Pat. No. 4,001,028 Frost et al. In the preparation of glass-ceramic products useful for coating ceramics, glass-ceramics or glass articles, it has been proposed to add one or more modifying oxides such as lead oxide, barium oxide, strontium oxide and calcium oxide (See U.S. Pat. No. 4,015,048 F. W. Martin). The control of sodium oxide and potassium oxide by replacing the clay by calcined kyanite or mullite has been proposed in U.S. Pat. No. 3,954,672, Somers et al, for making ceramic bodies such as turbine engine components, heat exchanger cores and furnace ware.
In U.S. Pat. No. 4,125,408, P. S. Peiper discloses the use of a high magnesium clay or saponite and tremolite in association with a kaolin type clay and alumina to produce a composition which can be fired at below 1300.degree. C. to produce a cordierite-like ceramic of low thermal expansion characteristics.